21623643 has 24 divisors (see below), whose sum is σ = 33508800. Its totient is φ = 13388544.

The previous prime is 21623639. The next prime is 21623663. The reversal of 21623643 is 34632612.

21623643 is a `hidden beast` number, since 2 + 16 + 2 + 3 + 643 = 666.

It is not a de Polignac number, because 21623643 - 2² = 21623639 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21623603) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 11193 + ... + 12981.

It is an arithmetic number, because the mean of its divisors is an integer number (1396200).

Almost surely, 2^21623643 is an apocalyptic number.

21623643 is a deficient number, since it is larger than the sum of its proper divisors (11885157).

21623643 is a wasteful number, since it uses less digits than its factorization.

21623643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1891 (or 1888 counting only the distinct ones).

The product of its digits is 5184, while the sum is 27.

The square root of 21623643 is about 4650.1229016016. The cubic root of 21623643 is about 278.5969050805.

The spelling of 21623643 in words is "twenty-one million, six hundred twenty-three thousand, six hundred forty-three".